Increased risk of skeletal fractures due to bone mass loss in aging or disease is a major clinical problem. Individual suffering and public health costs resulting from a projected increase in osteoporotic fractures as the U.S. population ages are motivating intensive research into the factors contributing to osteoporosis pathogenesis, identifying those individuals most at risk of fracture, and preventing the painful and debilitating fractures that result. While the majority of research has been focused on bone mass as a predictor of fracture risk (e.g., using DXA bone scans), this surrogate measure is non-specific in predicting bone strength. DXA bone density scanning, also called dual-energy x-ray absorptiometry or bone densitometry, is an enhanced form of x-ray technology that is used to measure bone loss. In particular, DXA is used for measuring bone mineral density (BMD).
Recent fracture epidemiology indicates that a great deal of fracture risk is independent of bone mass and subsequent research has focused on a group of bone characteristics loosely classified as bone quality. Among these qualities, bone geometry has been shown to be a significant and independent contributor to fracture risk. For example, in the proximal femur, longer hip axis length, larger neck shaft angle, larger neck diameter, and a wider femoral shaft have all been shown to correlate with increased fracture risk, though not all studies are consistent in their findings. This may be, in part, because these commonly used, simple geometry measures and DXA measured bone mass are not independent and may not completely explain the role of bone shape and density in controlling bone strength. In addition, it is likely that different combinations of bone shape and density distribution in humans can lead to similar bone strengths, as has been elegantly shown in the mouse model. From an engineering perspective, this is expected since structural strength arises from not only the amount of material in a structure (i.e., bone mass), but the combination of the shape of the structure, the intrinsic properties of the material, and the organization of that material within the structure. Thus, more comprehensive descriptions of bone shape and density distributions that give rise to bone strength may facilitate the identification of those at risk of bone fracture.